Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $246.75   10.527%   $272.7254   $272.73   $272.75   $272.70  
  Purchase #2 $24.62   6.358%   $26.1853   $26.19   $26.20   $26.20  
  Purchase #3 $199.85   4.430%   $208.7034   $208.70   $208.70   $208.70  
  Purchase #4 $46.43   13.689%   $52.7858   $52.79   $52.80   $52.80  
  Purchase #5 $242.44   11.175%   $269.5327   $269.53   $269.55   $269.50  
  Purchase #6 $208.91   12.238%   $234.4764   $234.48   $234.50   $234.50  
  Purchase #7 $204.81   11.450%   $228.2607   $228.26   $228.25   $228.30  
  7 purchase totals = $1,173.81       $1,292.6697   $1,292.68   $1,292.75   $1,292.70